In recent years, with regard to mobile telephones, together with portability when mobile, usage purposes include not only speaking but also have spread widely to include transmission and reception of electronic mail, internet connectivity, game functionality, and the like. As a result, in order to combine large screen display devices with operability for text input and the like, mobile telephones are being provided with various types of mechanisms.
For example, foldable mobile telephones are normally carried in a state with an upper casing and a lower casing folded, and by having the telephone in an open state when speaking or transmitting mail, various types of operation are possible by exposing a large screen display part and an operation part. With a foldable mobile telephone, it is possible to prevent mistaken operations when carrying by bringing together the display face and operation face when the telephone is folded, but on the other hand most operations cannot be done since the display face is not exposed when folded. As a result, there is a case where a small sized display part is separately provided with which it is possible to make confirmations in a folded state.
On the other hand, with a sliding type of mobile telephone, the display part is always exposed irrespective of whether the telephone is stored away or is extended, so that it is possible to check the display part in any state. For example, referring to FIG. 9, by providing a minimum key operation part 112 in a portion below the display part 111 in an upper casing 110, since the display part 111 is in an exposed state even when stored away, that is, when being carried, certain operations are possible in this state as it is, such as reading electronic mail and performing Internet operations, and convenience is improved. When performing operations such as creating a mail text, by sliding the upper casing 110 and the lower casing 120 in parallel, a key operation part 121 of the lower casing 120 hidden under the upper casing 110 is exposed and operations are possible. At this time, sliding operations are often performed manually, but in order to improve operability and operational feel, an assist mechanism supporting manual operation may be added to the slide mechanism. In such a case, since there is a necessity to generate a holding force at two positions, which are in an open state and in a closed state, in order to realize this simply, a spring may be configured in which load direction changes at an intermediate position. In general a compression spring or a spiral spring is used, and a mechanism that reverses load direction at an intermediate position is well known.
As a slide type mobile telephone having an assist mechanism in a slide mechanism, Patent Document 1, for example, discloses a configuration that uses an elastic force when a coil spring transforms into a U-shape, and a load direction at an intermediate position changes when a lower plate and an upper plate are made to slide. Patent Document 2 discloses a configuration having an intermediate portion that is wound and a coil shaped portion as an apex, to have a coil spring of an inverted V-shape with ends connected at left and right, and an expanding angular biasing force is used such that left and right connected ends of the coil spring tend to mutually separate, and a load direction changes at an intermediate position when a first member and a second member are made to slide. Patent Document 3 discloses a configuration that uses a peripheral direction biasing force of a spring so that load direction changes at an intermediate position when a first casing and a second casing are made to slide.    [Patent Document 1] JP Patent Kokai Publication No. JP-P2005-286994A    [Patent Document 2] JP Patent Kokai Publication No. JP-P2004-253526A    [Patent Document 3] JP Patent Kokai Publication No. JP-P2006-108881A